Deuterated analogs of etifoxine, their derivatives and uses thereof

ABSTRACT

This invention relates to deuterated analogs of etifoxine of Formula 1, solvates, prodrugs, and pharmaceutically acceptable salts thereof, as well as to methods for their preparation and use, and to pharmaceutical compositions. Briefly, this invention is generally directed to deuterated analogs of etifoxine as well as to methods for their preparation and use, and to pharmaceutical compositions containing the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/557,748, filed Sep. 12, 2017, which is a national stage entry ofPCT/US16/23231 filed Mar. 18, 2016, which claims benefit from U.S.Provisional Application Ser. No. 62/135,979, filed Mar. 20, 2015, whichare incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

Adsorption, distribution, metabolism and excretion (ADME) properties ofdrugs are critical characteristics of any drug and can mean thedifference between a safe and effective drug on the one hand, and aclinical and commercial failure, on the other hand. While recentadvances in drug formulation technologies (and drug conjugates orprodrugs) have offered some ability to improve ADME in limited cases,underlying ADME problems are still a major cause of the failure of drugsin clinical trials. A common ADME issue with currently approved drugsand drug candidates is rapid metabolism. A drug candidate that otherwiseis highly efficacious in in vitro and preclinical testing, can bemetabolized too quickly and cleared from the body giving little to nopharmacological effect. “Band Aid” efforts to overcome fast metabolisminclude dosing at very high levels or dosing very frequently. Both ofthese solutions to rapid metabolism are fraught with problems, includingincreasing the side effects of drugs, increasing exposure to toxicmetabolites, and decreasing patient dosing compliance due to frequency.

In limited cases, metabolic inhibitors have been used to improve thecharacteristics of a particular drug (see Kempf, D. et al. AntimicrobialAgents and Chemotherapy, 41(3), p. 654 (1997); Wang, L. et al. ClinicalPharmacology and Therapeutics, 56(6 Pt.1), p. 659 (1994). However, thisstrategy is not widely used, and can lead to serious unwanted sideeffects, and undesired drug-drug interactions.

Optimization of drug structure by chemists usually involves an iterativeprocess of structure modification to improve biological activity and/ormetabolic properties. However, a better metabolic profile often comes atthe expense of biological potency and efficacy, due to the significantstructural modifications of a desired pharmacophore structure needed tostop or slow biological degradation processes. A potential strategy forimproving the metabolic profile of a drug, without substantiallyaltering the biological potency and efficacy, is to replace (substitute)one or more hydrogen atoms with deuterium, thus slowing cytochrome P450mediated metabolism. Deuterium is an isotope of hydrogen that containsan additional neutron in its nucleus, and is safe, stable andnonradioactive. Due to the increased mass of deuterium as compared tohydrogen, the bond between carbon and deuterium has a higher energy(stronger) as compared to the bond between hydrogen and carbon, and canreduce metabolic reactions rates. The reduced metabolic reaction ratecan favorably impact a molecule's ADME properties, giving improvedpotency, efficacy, safety and tolerability. Other physicalcharacteristics of deuterium are essentially identical to hydrogen, andwould not be expected to have a biological impact on a molecule withdeuterium replacement.

In nearly four decades, only a small number of drugs have been approvedthat employ deuterium substitution to improve metabolism (see Blake, M.et al. J. Pharm. Sci., 64, p. 367 (1975); Foster, A. Adv. Drug Res., 14,p. 1 (1985); Kushner, D. et al. Can. J. Physiol. Pharmacol., p. 79(1999); Fisher M. et al. Curr. Opin. Drug Discov. Devel., 9, p. 101(2006)). The result of deuterium replacement of hydrogen on metabolicrate, however, has not been predictable and has led to variable results.In some cases the deuterated compounds had a decreased metabolicclearance in vivo, however for others, there was no change in theclearance rate, and yet others unexpectedly showed an increase inmetabolic clearance rate. This variability has led ADME experts toquestion or reject deuterium replacement as a strategic drug designmodification for reducing metabolic rate (see Foster and Fisher).

Even when a site and position of metabolism is known, deuteriumreplacement does not have a predictable effect on the metabolic rate. Itis only by preparation of the specific deuterium substituted drug(candidate) and testing that one can determine the extent of change inmetabolic rate. See Fukuto, J. et al. J. Med. Chem., 34(9), p. 2871(1991). Many, if not most, drug candidates have multiple sites wheremetabolism is possible, however, this is unique to each drug molecule,thus making deuterium replacement a different study for its effect oneach candidate. See Harbeson, L. and Tung, R. Medchem News, 2, p. 8(2014) and references therein. There are several examples of drugcandidates where deuterium substitution of hydrogen has led to anenhanced metabolic rate and/or metabolic switching, or no in vivo changeof the molecule's profile even after metabolic slowing. Harbeson et al.reveal that selective deuteration of paroxetine at predictedmetabolically labile positions actually produced analogs whichdemonstrated increased metabolism in vivo (Scott L. Harbeson and RogerD. Tung, Deuterium in Drug Discovery and Development, 46 annual reportin medicinal chemistry, 403-417 (2011)). Furthermore, Miwa reports thatdeuteration of metabolically labile sites may lead to the potentiation(or switching) of alternative metabolic pathways, with then undeterminedconsequences (Miwa, G., Lu, A., Kinetic Isotope Effects and ‘MetabolicSwitching’ in Cytochrome P450-Catalyzed Reactions, 7 Bioessays, 215-19(1987)). Phentermine has been deuterated to decrease its metabolic rate,however replacement of N,N-dimethyl hydrogens with deuterium resulted inno change observed (Allan B. Foster, “Deuterium Isotope Effects in theMetabolism of Drugs and Xenobiotics: Implications for Drug Design”,Advances in Drug Research, (14), 1-40 (1985)). Similarly, deuteration ofmetabolically active sites of tramadol led to no increase in duration ofeffect (Shao et. al., “Derivatives of Tramadol for Increased Duration ofEffect”, Bioorganic and Medicinal Chemistry Letters, (16), 691-94(2006)).

Etifoxine [6-chloro-2-(ethylamino)-4-methyl-4-phenyl-4H-3,1-benzoxazine]was originally disclosed in U.S. Pat. No. 3,725,404 by Hoffmann, I etal. Etifoxine has been shown to be an effective, acute acting,anxiolytic agent in humans with minimal sedative and ataxic sideeffects. Stein, D., Adv. Ther. 32(1), p. 57 (2015); Nguyen, N. et al.,Hum. Psychopharm. 21, p. 139 (2006); Micallef, J., Fundam. Clin.Pharmacol., 15(3), p. 209 (2001).

The hydrochloride salt of etifoxine[6-chloro-2-(ethylamino)-4-methyl-4-phenyl-4H-3,1-benzoxazine] is knownas Stresam™ and is sold mainly in France and in a limited number ofother markets around the world for the treatment of anxiety(specifically, anxiety with somatic manifestations). The short half-lifeof etifoxine in humans (4-6 hours) is a significant limitation in itsuse. The recommended dosing schedule for etifoxine is three times a day(or a higher dose, twice a day). This schedule can be quite inconvenientto the patient and can contribute to dosing noncompliance. See Santana,L. et al, Patient Preference and Adherence, 5, p. 427 (2011). Studiesalso show a significant individual variability of the pharmacokineticparameters especially in the dose C_(max) relationship. (see etifoxinepackage insert information, Lundbeck Argentina SA). Inter andintra-patient variability is largely based on differences in drugmetabolic capacity. Reducing inter and intra-patient variability isdesirable as it hampers optimal therapy. Poor metabolizers may be athigher risk of off-targets side-effects due to higher drug levels.Excessive metabolizers may not get relief from insufficient efficacy dueto excessively diminished drug levels. (see Wilkinson, G. The NewEngland Journal of Medicine (352), 2211-21 (2005). Enhancing themetabolic stability of etifoxine will reduce inter- and intra-patientvariability as metabolic capacity becomes less of a determining factor.

Consequently, despite the desirable and beneficial effects of etifoxine,the requirements for multiple daily dosing and significant drug levelpatient variability limit its advantages. Thus, there is a continuingneed for new compounds to treat the aforementioned diseases andconditions.

SUMMARY OF THE INVENTION

Briefly, this invention is generally directed to deuterated analogs ofetifoxine as well as to methods for their preparation and use, and topharmaceutical compositions containing the same. More specifically, thedeuterated analogs of etifoxine of this invention are compoundsrepresented by the general structure:

including pharmaceutically acceptable salts, solvates, and prodrugsthereof, wherein each X¹, X², X³ are independently selected from thegroup consisting of hydrogen and deuterium.

The present invention also is directed to pharmaceutical formulationswhich include a compound of Formula I, pharmaceutically acceptablesalts, solvates, and prodrugs thereof, and one or more pharmaceuticallyacceptable excipients, carriers or diluents. Such formulations contain atherapeutically effective amount of a compound of Formula I,pharmaceutically acceptable salts, solvates, and prodrugs thereof, andone or more pharmaceutically acceptable excipients, carriers ordiluents.

The present invention is also directed to pharmaceutical compositionsfor the treatment of conditions amenable to modulation of the GABA_(A)receptor complex; or increasing endogenous neurosteroid and neuroactivesteroid levels; CNS disorders; PNS disorders; or inflammatory conditionscomprising administering to a subject in need of such treatment atherapeutically effective amount of a compound of Formula I, andpharmaceutically acceptable salts, solvates, and prodrugs thereof.

The present invention is also directed to the use of compounds ofFormula I, pharmaceutically acceptable salts, solvates, and prodrugsthereof to treat conditions amenable to modulation of the GABA_(A)receptor complex; or increasing endogenous neurosteroid and neuroactivesteroid levels; CNS disorders; PNS disorders; or inflammatory conditionsas described more fully below in subjects in need of such therapycomprising administering a therapeutically effective amount of suchcompounds.

In another aspect, the invention also provides a kit comprising atherapeutically effective amount of a compound of Formula I, or apharmaceutically acceptable salt, solvate, or prodrug thereof, andinstructions for treating a human patient suffering from conditionsamenable to modulation of the GABA_(A) receptor complex; or increasingendogenous neurosteroid and neuroactive steroid levels; CNS disorders;PNS disorders; or inflammatory conditions as described more fully below.

Additional embodiments and advantages of the invention will be set forthin part in the description that follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The embodiments and advantages of the invention will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims. It is to be understood that both theforegoing general description and the following detailed description areexemplary and explanatory only and are not restrictive of the invention,as claimed. All texts and references cited herein are incorporated byreference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the mean plasma concentration-time profiles of etifoxineand the compound of Example 1 after a PO dose of 50 mg/kg in maleSprague-Dawley rats.

DETAILED DESCRIPTION

The present invention is directed to deuterated analogs of etifoxinethat have the therapeutic effects of etifoxine but with surprisinglysuperior ADME properties.

Etifoxine has been studied extensively preclinically, and hasdemonstrated efficacy in many animal models of CNS and mental disorderssuch as anxiety, pain, inflammatory pain, nerve damage, MultipleSclerosis, alcohol withdrawal, epilepsy and light-induced lesions of theretina. Verleye, M. et al., Pharmacol. Biochem. Behay., 82(4), p. 712(2005); Ugale, R. et al., Brain Res., 12, p. 193 (2007); Verleye, M. etal., Alcohol, 43(3), p. 197 (2009); Aouad, M. et al., Pain, 147(1-3), p.54 (2009); Girard, C. et al., J. Neuroendocrinol., 24(1), p. 71 (2012);Zhou, X. et al., Mol. Med. Rep., 8(1), p. 75 (2013); Aouad, M. et al.,Eur. J. Pain, 18(2), p. 258 (2014); Aouad, M. et al., Pain, 155(2), p.408 (2014); Zhou, X. et al., Muscle Nerve, 50(2), p. 235 (2014); Dai, T.et al., J. Reconstr. Microsurg., 30(6), p. 381 (2014); Juif, P. et al.,Neuropharmacology, 91, p. 117 (2015), Verleye, M et al. WO 2015113991.

Etifoxine has been described in scientific literature to act throughallosteric modulation of the GABA_(A) ion channel complex as well asincreasing the levels of endogenous neurosteroids and neuroactivesteroids. Verleye, M. et al., Neuroreport., 10(15), p. 3207 (1999);Verleye, M. et al., Neurosci. Lett., 301(3), p. 191 (2001); Hamon, A. etal., Neuropharmacology, 45(3), p. 293 (2003); Ugale, R. et al., BrainRes., 12, p. 193 (2007); Verleye, M. et al., Pharmacol. Biochem. Behay.,82(4), p. 712 (2005).

Neurosteroids and neuroactive steroids have demonstratedanti-inflammatory activity, for instance progesterone andallopregnanolone reduce both cytokines IL-1.beta. and TNF-.alpha. in amodel of TBI (see He, J. et al. Experimental Neurology, 189, p. 404(2004)). Furthermore, dehydroepiandosterone (DHEA), which is mainlysynthesized in the adrenal glands, inhibits the synthesis of cytokinesIL-6 and TNF (see Straub, R. Rheumatology, 39, p. 624 (1999). Byincreasing levels of neurosteroids and/or neuroactive steroids, it isthought that etifoxine may be effective in treating neuroinflammation,peripheral inflammation and a variety of inflammatory conditions.

Neurosteroids and neuroactive steroids have been shown to beneuroregenerative and neuroprotective in preclinical models, seeBrinton, R. Nature Reviews Endocrinology 9, 241-250 (2013) and Borowicz,K. et. al. Frontiers in Endocrinology 2(50), P. 1 (2011). Likewise,etifoxine has also demonstrated neuroregenerative and neuroprotectiveeffects preclinically (Girard et. al. Journal of Neuroendocrinology 24,71-81 (2011), Girard et. al. Clinical and Experimental Pharmacology andPhysiology 36, 655-661 (2009), Zhou et. al. Muscle Nerve. 50(2):235-43(2014)).

While the present invention is not limited to a precise mechanism ofaction, deuterated analogs of etifoxine can be used in the treatment ofconditions associated with the need for neuroprotection includingneurodegeneration and neuroregeneration, and conditions associated withnerve degeneration and nerve dysfunction, as well as inflammatoryconditions.

In one aspect, the present invention is directed to a compound ofFormula I:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof,wherein: each of X¹, X² and X³ is independently selected from the groupconsisting of hydrogen and deuterium.

Definitions

Unless specifically noted otherwise herein, the definitions of the termsused are standard definitions used in the art of organic synthesis andpharmaceutical sciences.

The articles “a” and “an” are used herein to refer to one or more thanone (i.e. to at least one) of the grammatical object of the article. Byway of example, “an element” means one element or more than one element.

As used herein, the term “or” is generally employed in the sense asincluding “and/or” unless the context of the usage clearly indicatesotherwise.

Where the plural form is used for compounds, salts and the like, this istaken to mean also a single compound, salt, or the like.

As used herein “solvate” refers to a complex of variable stoichiometryformed by a solute (e.g. a compound of formula (I) or a salt, ester orprodrug thereof) and a solvent. Such solvents for the purpose of theinvention may not interfere with the biological activity of the solute.Examples of suitable solvents include water, methanol, ethanol andacetic acid. Generally the solvent used is a pharmaceutically acceptablesolvent. Examples of suitable pharmaceutically acceptable solventsinclude water, ethanol and acetic acid. Generally the solvent used iswater.

“Isomers” mean any compound with an identical molecular formula buthaving a difference in the nature or sequence of bonding or arrangementof the atoms in space. Examples of such isomers include, for example, E-and Z-isomers of double bonds, enantiomers, and diastereomers. Compoundsof the present invention depicting a bond with a straight line, unlessspecifically noted otherwise, is intended to encompass a single isomerand/or both isomers and means any compound with an identical molecularformula but having a difference in the nature or sequence of bonding orarrangement of the atoms in space.

The term “GABA_(A) receptor” refers to a protein complex that detectablybinds GABA and mediates a dose dependent alteration in chlorideconductance and membrane polarization. Receptors comprisingnaturally-occurring mammalian (especially human or rat) GABA_(A)receptor subunits are generally preferred, although subunits may bemodified provided that any modifications do not substantially inhibitthe receptor's ability to bind GABA (i.e., at least 50% of the bindingaffinity of the receptor for GABA is retained). The binding affinity ofa candidate GABA_(A) receptor for GABA may be evaluated using a standardligand binding assay known in the art. There are a variety of GABA_(A)receptor subtypes that fall within the scope of the term “GABA_(A)receptor.” These subtypes include, but are not limited to α₁₋₆, β₁₋₃,γ₁₋₃, θ, ε, δ and σ₁₋₃ receptor subtypes. GABA_(A) receptors may beobtained from a variety of sources, such as from preparations of ratcortex or from cells expressing cloned human GABA_(A) receptors.Particular subtypes may be readily prepared using standard techniques(e.g., by introducing mRNA encoding the desired subunits into a hostcell).

As used herein, a “CNS disorder” is a disease or condition of thecentral nervous system that can be treated, prevented, managed orameliorated with a compound or composition provided herein. Certain CNSdisorders are responsive to GABA_(A) receptor modulation in a subjectand some CNS disorders are responsive to increasing endogenousneurosteroids and neuroactive steroids. Some CNS disorders includecomponents where the Peripheral Nervous System (“PNS”) is alsocompromised. Exemplary CNS disorders include multiple sclerosis, spinalmuscular atrophy (believed to be due to loss of function of neuronalcells in the anterior horn of the spinal cord), muscle relaxation inspinal spasticity, cerebral palsy, trigeminal neuralgia, migraine,Alzheimer's disease, Huntington's chorea, Parkinson's disease,Creutzfeldt-Jakob's disease, Friedreich disease, retinal degenerationsand photo-induced damage to the retina including photoretinitis,retinitis pigmentosa, age-related macular degeneration (AMD) and maculardegeneration, delirium, dementia and amnestic and other cognitivedisorders (delirium; dementia, such as dementia of Alzheimer's type,vascular dementia, dementia due to HIV disease, dementia due to headtrauma, dementia due to Parkinson's disease, dementia due toHuntington's disease, dementia due to Pick's disease, dementia due toCreutzfeldt-Jakob disease, dementia due to general medical condition,substance-induced dementia, dementia due to multiple etiologies,dementia NOS (hereinafter “not otherwise specified” is abbreviated NOS);amnestic disorders, (such as amnestic disorder due to general medicalcondition, substance-induced amnestic disorder, amnestic disorder NOS;cognitive disorder NOS); ischemic or hemorrhagic cerebral vascularincidents including stroke and traumatic brain injury (TBI),phakomatoses (particularly neurofibromatosis), amyotrophic lateralsclerosis, schizophrenia, mood disorders (such as depressive disorder,including major depressive disorder-single episode or recurrent,dysthymic disorder, depressive disorder NOS; bipolar disorder,including. bipolar I disorder, bipolar II disorder, cyclothymicdisorder, bipolar disorder NOS, mood disorder due to general medicalcondition, substance-induced mood disorder, mood disorder NOS), drugwithdrawal symptoms, stuttering, autism, autism spectrum disorders, andconvulsive disorders such as epilepsy. CNS disorders also includesmental disorders described in the American Psychiatric Association'sDiagnostic and Statistical Manual of Mental Disorders, 5th edition(DSM-V) and include anxiety disorders (panic disorder withoutagoraphobia, panic disorder with agoraphobia, agoraphobia withouthistory of panic disorder, specific phobia, social phobia, obsessivecompulsive disorder, posttraumatic stress disorder, acute stressdisorder, generalized anxiety disorder, anxiety disorder due to amedical condition, substance induced anxiety disorder, anxiety disordernot otherwise specified (NOS)), mood disorders, sleep disorders (primarysleep disorder, e.g. primary insomnia, primary hypersomnia, narcolepsy,breathing-related sleep disorder, circadian rhythm sleep disorder,dysomnia NOS; parasomnia, including. nightmare disorder, sleep terrordisorder, sleepwalking disorder, parasomnia NOS; sleep disordersecondary to another mental disorder, e.g. sleep disorder secondary toanxiety, mood disorder and/or other mental disorder; sleep disorder dueto general medical condition and substance-induced sleep disorder),attention deficit, attention deficit hyperactivity, and disruptivebehavior disorders (attention deficit/hyperactivity disorder—combinedtype, predominantly inattentive type and predominantlyhyperactive-impulsive type; attention deficit/hyperactivity disorderNOS; conduct disorder, oppositional defiant disorder and disruptivebehavior disorder NOS) and substance related disorders. Mental disordersalso include eating disorders such as anorexia and bulimia. Furthermental disorders and criteria for those disorders are described in theAmerican Psychiatric Association's Diagnostic and Statistical Manual ofMental Disorders, 5.sup.th edition (DSM-V), the contents of which arehereby incorporated by reference in their entirety.

As used herein, a “PNS disorder” is a disease or condition of theperipheral nervous system that can be treated, prevented, managed orameliorated with a compound or composition provided herein. Certain PNSdisorders are responsive to increasing endogenous neuroactive steroids.Some PNS disorders involve motor nerve and/or sensory nerve dysfunctionand can include components where the spinal cord and/or the brain arealso compromised. Exemplary PNS disorders include neuropathic disorders(neuropathic disorders include neuropathies associated with a metabolicdisturbance such as diabetic neuropathy, drug-induced neuropathies suchas alcohol induced neuropathy and vincristine-induced neuropathy,neuropathies associated with an inflammatory process as inGuillain-Barre syndrome, neuropathies associated with enzyme deficiencyas in Fabry's disease and Krabbe's disease, peripheral neuropathy,infectious neuropathic conditions such as post-herpetic and HIV-inducedneuralgia, hereditary motor and sensory neuropathies such asCharcot-Marie-Tooth disease), and radiculoneuropathic diseases.

As used herein, a “neurodegenerative process” is characterized by thedysfunction and death of the neurons leading to the loss of theneurological functions mediated by the brain (CNS), the spinal cord andthe PNS. They can result, amongst others, from pathological situationsknown collectively under the term of neurodegenerative diseases oraffections, traumatism, or exposure to toxins.

As used herein, a “neuroprotective property” is the ability of acompound of the invention to treat a neurodegenerative process.

As used herein and unless otherwise indicated, the terms “neurosteroids”and “neuroactive steroids” refer to steroids naturally produced in asubject and alter neuronal excitability through interaction withligand-gated ion channels and other cell surface receptors.Neurosteroids are produced in the brain. Neuroactive steroids areproduced by conversion of peripherally-derived adrenal steroids orgonadal steroids. Examples of neurosteroids and neuroactive steroidsare: pregnenolone, pregnanolone, allopregnanolone,tetrahydrodeoxycorticosterone, dehydroepiandrosterone and progesterone.Neuroactive steroids can have effects in the CNS and peripherally.

The term “treat” as used herein means decrease, reverse, suppress,attenuate, diminish, arrest, or stabilize the development or progressionof a disease (including., a disease or disorder delineated herein),lessen the severity of the disease or improve the symptoms associatedwith the disease. In one aspect, treatment does not include prevention.

“Disease” means any condition or disorder that damages or interfereswith the normal function of a cell, tissue, or organ.

As used herein “subject” is an animal, typically a mammal, includinghuman, such as a patient.

As used herein, and unless otherwise specified, the terms“therapeutically effective amount” and “effective amount” of a compoundrefer to an amount sufficient to provide a therapeutic benefit in thetreatment, prevention and/or management of a disease, to delay orminimize one or more symptoms associated with the disease or disorder tobe treated. The terms “therapeutically effective amount” and “effectiveamount” can encompass an amount that improves overall therapy, reducesor avoids symptoms, or causes of disease or disorder, or enhances thetherapeutic efficacy of another therapeutic agent.

The terms “co-administration” and “in combination with” include theadministration of two therapeutic agents (for example, compounds of thisinvention and lorazepam) either simultaneously, concurrently orsequentially with no specific time limits. In one embodiment, bothagents are present in a subject at the same time or exert theirbiological or therapeutic effect at the same time. In one embodiment,the two therapeutic agents are in the same composition or unit dosageform. In another embodiment, the two therapeutic agents are in separatecompositions or unit dosage forms.

It will be recognized that some variation of natural isotopic abundanceoccurs in a synthesized compound depending upon the origin of chemicalmaterials used in the synthesis. Thus, a preparation of etifoxine willinherently contain small amounts of deuterated isotopologues. Theconcentration of naturally abundant stable hydrogen and carbon isotopes,notwithstanding this variation, is small and immaterial as compared tothe degree of stable isotopic substitution of compounds of thisinvention. See, for instance, Wada, E et al., Seikagaku, 1994, 66:15;Gannes, L Z et al., Comp Biochem Physiol Mol lntegr Physiol, 1998,119:725.

In the compounds of this invention, any atom not specifically designatedas a particular isotope is meant to represent any stable isotope of thatatom. Unless otherwise stated, when a position is designatedspecifically as “H” or “hydrogen”, the position is understood to havehydrogen at its natural abundance isotopic composition. Also, unlessotherwise stated, when a position is designated specifically as “D” or“deuterium”, the position is understood to have deuterium at anabundance that is at least 3340 times greater than the natural abundanceof deuterium, which is 0.015% (i.e., at least 50.1% incorporation ofdeuterium).

The term “isotopic enrichment factor” as used herein means the ratiobetween the isotopic abundance and the natural abundance of a specifiedisotope. In some embodiments, a compound of this invention has anisotopic enrichment factor for each designated deuterium atom of atleast 3500 (52.5% deuterium incorporation at each designated deuteriumatom), at least 4000 (60% deuterium incorporation), at least 4500 (67.5%deuterium incorporation), at least 5000 (75% deuterium), at least 5500(82.5% deuterium incorporation), at least 6000 (90% deuteriumincorporation), at least 6333.3 (95% deuterium incorporation), at least6466.7 (97% deuterium incorporation), at least 6533 (98% deuteriumincorporation), at least 6600 (99% deuterium incorporation), or at least6633.3 (99.5% deuterium incorporation).

The term “isotopologue” refers to a species that differs from a specificcompound of this invention only in the isotopic composition thereof.

The term “compound,” when referring to a compound of this invention,refers to a collection of molecules having an identical chemicalstructure, except that there may be isotopic variation among theconstituent atoms of the molecules. Thus, it will be clear to those ofskill in the art that a compound represented by a particular chemicalstructure containing indicated deuterium atoms, will also contain lesseramounts of isotopologues having hydrogen atoms at one or more of thedesignated deuterium positions in that structure. The relative amount ofsuch isotopologues in a compound of this invention will depend upon anumber of factors including the isotopic purity of deuterated reagentsused to make the compound and the efficiency of incorporation ofdeuterium in the various synthesis steps used to prepare the compound.However, as set forth above, the relative amount of such isotopologuesin total will be less than 49.9% of the compound. In other embodiments,the relative amount of such isotopologues in total will be less than47.5%, less than 40%, less than 32.5%, less than 25%, less than 17.5%,less than 10%, less than 5%, less than 3%, less than 1%, or less than0.5% of the compound.

The term “pharmaceutically acceptable,” as used herein, refers to acomponent that is, within the scope of sound medical judgment, suitablefor use in contact with the tissues of humans and other mammals withoutundue toxicity, irritation, allergic response and the like, and arecommensurate with a reasonable benefit/risk ratio. A “pharmaceuticallyacceptable salt” means any non-toxic salt that, upon administration to arecipient, is capable of providing, either directly or indirectly, acompound of this invention. A “pharmaceutically acceptable counterion”is an ionic portion of a salt that is not toxic when released from thesalt upon administration to a recipient. Acids commonly employed to formpharmaceutically acceptable salts include inorganic acids such ashydrogen bisulfide, hydrochloric acid, hydrobromic acid, hydroiodicacid, sulfuric acid and phosphoric acid, as well as organic acids suchas para-toluenesulfonic acid, salicylic acid, tartaric acid, bitartaricacid, ascorbic acid, maleic acid, besylic acid, fumaric acid, gluconicacid, glucuronic acid, formic acid, glutamic acid, methanesulfonic acid,ethanesulfonic acid, benzenesulfonic acid, lactic acid, oxalic acid,para-bromophenylsulfonic acid, carbonic acid, succinic acid, citricacid, benzoic acid and acetic acid, as well as related inorganic andorganic acids. Such pharmaceutically acceptable salts thus includesulfate, pyrosulfate, bisulfate, sulfite, bisulfite, phosphate,monohydrogenphosphate, dihydrogenphosphate, metaphosphate,pyrophosphate, chloride, bromide, iodide, acetate, propionate,decanoate, caprylate, acrylate, formate, isobutyrate, caprate,heptanoate, propiolate, oxalate, malonate, succinate, suberate,sebacate, fumarate, maleate, butyne-1,4-dioate, hexyne-1,6-dioate,benzoate, chlorobenzoate, methylbenzoate, dinitrobenzoate,hydroxybenzoate, methoxybenzoate, phthalate, terephthalate, sulfonate,xylene sulfonate, phenylacetate, phenylpropionate, phenylbutyrate,citrate, lactate, .beta.-hydroxybutyrate, glycolate, maleate, tartrate,methanesulfonate, propanesulfonate, naphthalene-1-sulfonate,naphthalene-2-sulfonate, mandelate and other salts. In one embodiment,pharmaceutically acceptable acid addition salts include those formedwith mineral acids such as hydrochloric acid and hydrobromic acid, andespecially those formed with organic acids such as maleic acid. Standardmethods for the preparation of pharmaceutically acceptable salts andtheir formulations are well known in the art, and are disclosed invarious references, including for example, “Remington: The Science andPractice of Pharmacy”, A. Gennaro, ed., 20th edition, Lippincott,Williams & Wilkins, Philadelphia, Pa.

The compounds of the present invention (including., compounds of FormulaI), may contain an asymmetric carbon atom, for example, as the result ofdeuterium substitution or otherwise. As such, compounds of thisinvention can exist as either individual enantiomers, or mixtures of thetwo enantiomers. Accordingly, a compound of the present invention mayexist as either a racemic mixture or a scalemic mixture, or asindividual respective stereoisomers that are substantially free fromanother possible stereoisomer. The term “substantially free of otherstereoisomers” as used herein means less than 25% of otherstereoisomers, preferably less than 10% of other stereoisomers, morepreferably less than 5% of other stereoisomers and most preferably lessthan 2% of other stereoisomers, or less than “X”% of other stereoisomers(wherein X is a number between 0 and 100, inclusive) are present.Methods of obtaining or synthesizing an individual enantiomer for agiven compound are known in the art and may be applied as practicable tofinal compounds or to starting material or intermediates.

Unless otherwise indicated, when a disclosed compound is named ordepicted by a structure without specifying the stereochemistry and hasone or more chiral centers, it is understood to represent all possiblestereoisomers of the compound.

The term “stable compounds,” as used herein, refers to compounds whichpossess stability sufficient to allow for their manufacture and whichmaintain the integrity of the compound for a sufficient period of timeto be useful for the purposes detailed herein (including., formulationinto therapeutic products, intermediates for use in production oftherapeutic compounds, isolatable or storable intermediate compounds,treating a disease or condition responsive to therapeutic agents).

“D” and “d” both refer to deuterium. Unless otherwise indicated,“stereoisomer” refers to both enantiomers and diastereomers.

The term “optionally substituted with deuterium” means that one or morehydrogen atoms in the referenced moiety may be replaced with acorresponding number of deuterium atoms.

The present invention includes prodrugs of the compounds of Formula Iabove. In general, such prodrugs will be functional derivatives of thecompounds of Formula I that are readily convertible in vivo into therequired compound of Formula I. Conventional procedures for theselection and preparation of suitable prodrug derivatives are described,for example, in Design of Prodrugs, ed. H. Bundgaard, Elsevier, 1985.Such prodrugs include but are not limited to ester prodrugs fromalcohols and acids and phosphate prodrugs of alcohols. The prodrug canbe formulation to achieve a goal of improved chemical stability,improved patient acceptance and compliance, improved bioavailability,prolonged duration of action, improved organ selectivity, improvedformulation (including., increased hydrosolubility), and/or decreasedside effects (including., toxicity).

Where the compounds of the present invention have at least oneasymmetric center, they may accordingly exist as enantiomers. Where thecompounds possess two or more asymmetric centers, they may additionallyexist as diastereoisomers. Specifically, etifoxine exists as a racemicmixture and R-Etifoxine and S-Etifoxine have been prepared. U.S. Pat.No. 8,110,569. The present invention includes deuterated analogs ofR-Etifoxine and deuterated analogs of S-Etifoxine. It is to beunderstood that all such stereoisomers and mixtures thereof in anyproportion are encompassed within the scope of the present invention.Where the compounds possess geometrical isomers, all such isomers andmixtures thereof in any proportion are encompassed within the scope ofthe present invention. Tautomers of the compounds of the invention areencompassed by the present application. Thus, for example, a carbonylincludes its enol tautomer.

As used herein “pure S-etifoxine” are deuterated analogs that are issubstantially free from deuterated R-etifoxine analogs (i.e., inenantiomeric excess). In other words, the “S” form of the deuteratedetifoxine is substantially free from the “R” form of the compound andis, thus, in enantiomeric excess of the “R” form.

The term “enantiomerically pure” or “pure enantiomer” denotes that thecompound comprises more than 75% by weight, more than 80% by weight,more than 85% by weight, more than 90% by weight, more than 91% byweight, more than 92% by weight, more than 93% by weight, more than 94%by weight, more than 95% by weight, more than 96% by weight, more than97% by weight, more than 98% by weight, more than 98.5% by weight, morethan 99% by weight, more than 99.2% by weight, more than 99.5% byweight, more than 99.6% by weight, more than 99.7% by weight, more than99.8% by weight or more than 99.9% by weight, of the enantiomer. Incertain embodiments, the weights are based upon total weight of thedeuterated etifoxine analog.

As used herein and unless otherwise indicated, the term“enantiomerically pure R-etifoxine” refers to the deuterated analog thatat least about 80% by weight deuterated R-etifoxine and at most about20% by weight deuterated S-etifoxine, at least about 90% by weightdeuterated R-etifoxine and at most about 10% by weight deuteratedS-etifoxine, at least about 95% by weight deuterated R-etifoxine and atmost about 5% by weight deuterated S-etifoxine, at least about 99% byweight deuterated R-etifoxine and at most about 1% by weight deuteratedS-etifoxine, at least about 99.9% by weight deuterated R-etifoxine or atmost about 0.1% by weight deuterated S-etifoxine. In certainembodiments, the weights are based upon total weight of deuteratedetifoxine analog.

As used herein and unless otherwise indicated, the term“enantiomerically pure 5-etifoxine” refers to at least about 80% byweight deuterated S-etifoxine and at most about 20% by weight deuteratedR-etifoxine, at least about 90% by weight deuterated S-etifoxine and atmost about 10% by weight deuterated R-etifoxine, at least about 95% byweight deuterated S-etifoxine and at most about 5% by weight deuteratedR-etifoxine, at least about 99% by weight deuterated S-etifoxine and atmost about 1% by weight deuterated R-etifoxine or at least about 99.9%by weight deuterated S-etifoxine and at most about 0.1% by weightdeuterated R-etifoxine. In certain embodiments, the weights are basedupon total weight of deuterated etifoxine analog.

Therapeutic Compounds

In one aspect, the present invention is directed to compounds of FormulaIA:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof,wherein:

each X¹, X², X³, X⁴, X⁵ and X⁶ are independently selected from hydrogenand deuterium. In one embodiment, in such compounds each X.sup.1 isdeuterium.

In one embodiment of this invention, X¹, X², X³, X⁴, X⁵ and X⁶ arehydrogen such that the deuterated analog of etifoxine is a compoundhaving the structure of Formula IIA:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In one embodiment, the compounds of Formula IA have each X.sup.1 ishydrogen. In one such embodiment of this invention, X¹, X², X³, X⁴, X⁵and X⁶ are hydrogen such that the deuterated analog of etifoxine is acompound having the structure of Formula IIIA:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In one embodiment, the compounds of Formula IA have each X¹ and each X⁶as deuterium. In one such embodiment of this invention, X², X³, X⁴ andX⁵ are hydrogen such that the deuterated analog of etifoxine is acompound having the structure of Formula IVA:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In one embodiment, compounds of Formula IA have each X.sup.1 and eachX.sup.5 are deuterium. In one such embodiment, X², X³, X⁴, and X⁶ arehydrogen such that the deuterated analog of etifoxine is a compoundhaving the structure of Formula VA:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In one embodiment, compounds of Formula IA have each X.sup.1, X.sup.2,X.sup.3, X.sup.4, and X.sup.6 are deuterium. In one such embodiment ofthis invention, X.sup.5 and X.sup.6 are hydrogen such that thedeuterated analog of etifoxine is a compound having the structure ofFormula VIA:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In one embodiment of the invention, compounds of Formula IA have eachX¹, X⁵, and X⁶ are deuterium. In one such embodiment of this invention,X⁴, X³, and X⁴ are hydrogen such that the deuterated analog of etifoxineis a compound having the structure of Formula VIIA:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In one aspect, the present invention is directed to compounds of FormulaI:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof,wherein: each of X¹, X², and X³ are independently selected from hydrogenand deuterium. In one embodiment, in such compounds each X¹ isdeuterium.

In one embodiment of this invention, each X² and X³ are hydrogen suchthat the deuterated analog of etifoxine is a compound having thestructure of Formula II:

and pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In one embodiment of this invention the deuterated analog of etifoxineis6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amineand pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In another embodiment of this invention the deuterated analog ofetifoxine is6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-(phenyl-d.sub.5)-4H-3,1-benzoxazin-2-amineand pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In yet another embodiment of this invention the deuterated analog ofetifoxine is6-chloro-N-(ethyl-d.sub.5)-4-(methyl-d.sub.3)-4-(phenyl-d.sub.5)-4H-3,1-b-enzoxazin-2-amineand pharm-aceutically acceptable salts, solvates, and prodrugs thereof.

In yet another embodiment of this invention the deuterated analog ofetifoxine is6-chloro-N-(ethyl-1,1-d.sub.2)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amin-eand pharmaceutically acceptable salts, solvates, and prodrugs thereof.

In some embodiments, a compound of Formulae I-II;6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amine;6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-(phenyl-d.sub.5)-4H-3,1-benzoxazin-2-amine;6-chloro-N-(ethyl-d.sub.5)-4-(methyl-d.sub.3)-4-(phenyl-d.sub.5)-4H-3,1-benzoxazin-2-amine;or6-chloro-N-(ethyl-1,1-d.sub.2)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amin-ehas an isotopic enrichment factor for each designated deuterium atom ofat least 3500 (52.5% deuterium incorporation at each designateddeuterium atom), at least 4000 (60% deuterium incorporation), at least4500 (67.5% deuterium incorporation), at least 5000 (75% deuterium), atleast 5500 (82.5% deuterium incorporation), at least 6000 (90% deuteriumincorporation), at least 6333.3 (95% deuterium incorporation), at least6466.7 (97% deuterium incorporation), at least 6533 (98% deuteriumincorporation), at least 6600 (99% deuterium incorporation), or at least6633.3 (99.5% deuterium incorporation).

In one aspect, the compounds of Formulae I-II, are enantiomerically puredeuterated S-etifoxine isomer. In the compositions provided herein,deuterated enantiomerically pure S-etifoxine analog or apharmaceutically acceptable salt, solvate, or prodrug thereof can bepresent with other active or inactive ingredients. For example, apharmaceutical composition comprising deuterated enantiomerically pureS-etifoxine analog can comprise, for example, about 90% excipient andabout 10% enantiomerically pure deuterated S-etifoxine analog. Incertain embodiments, the enantiomerically pure S-etifoxine deuteratedanalog in such compositions can, for example, comprise, at least about99.9% by weight S-etifoxine deuterated analog and at most about 0.1% byweight R-etifoxine deuterated analog. In certain embodiments, the activeingredient can be formulated with little or no excipient or carrier.

In one aspect, the compounds of Formulae I-II, are enantiomerically puredeuterated R-etifoxine isomer. In the compositions provided herein,deuterated enantiomerically pure R-etifoxine analog or apharmaceutically acceptable salt, solvate, or prodrug thereof can bepresent with other active or inactive ingredients. For example, apharmaceutical composition comprising deuterated enantiomerically pureR-etifoxine analog can comprise, for example, about 90% excipient andabout 10% enantiomerically pure deuterated R-etifoxine analog. Incertain embodiments, the enantiomerically pure R-etifoxine deuteratedanalog in such compositions can, for example, comprise, at least about99.9% by weight R-etifoxine deuterated analog and at most about 0.1% byweight R-etifoxine deuterated analog. In certain embodiments, the activeingredient can be formulated with little or no excipient or carrier.

In another aspect, the compounds of the invention wherein any atom notdesignated as deuterium is present at its natural isotopic abundance.

In another aspect, there is provided pharmaceutical compositionscomprising a pharmaceutically acceptable excipient and a compound ofFormulae I-II, and pharmaceutically acceptable salts, solvates, andprodrugs thereof.

Methods of Treatment

In one embodiment, a compound of the invention of Formulae I-II, andpharmaceutically acceptable salts, solvates, and prodrugs thereof, isadministered to a subject in an amount effective to modulate theGABA_(A) receptor.

In one embodiment, a compound of the invention of Formulae I-II, andpharmaceutically acceptable salts, solvates, and prodrugs thereof, isadministered to a subject in an amount effective to increaseneurosteroids and/or neuroactive steroids.

In one embodiment, the compounds or composition of this invention actsas a modulator of GABA_(A) receptor complex and increases endogenousneuroactive steroids and has anxiolytic, and/or anticonvulsant, and/orsedative/hypnotic, and/or anesthetic properties, and/or neuroprotectiveproperties.

In certain embodiments, provided herein are methods of treating orpreventing an etifoxine responsive condition comprising administering toa subject in need thereof a therapeutically effective amount of acompound of Formulae I-II, and pharmaceutically acceptable salts,solvates, and prodrugs thereof.

In one embodiment, compounds of Formulae I-II, and pharmaceuticallyacceptable salts, solvates, and prodrugs thereof are used to treat CNSdisorders, PNS disorders, and/or inflammatory conditions byadministering to a subject in need thereof a therapeutically effectiveamount.

In one embodiment, compounds of Formulae I-II, and pharmaceuticallyacceptable salts thereof are used to treat CNS disorders. In suchembodiments, CNS disorders include multiple sclerosis, muscle relaxationin spinal spasticity, retinal degenerations and photo-induced damage tothe retina including photoretinitis, retinitis pigmentosa, age-relatedmacular degeneration (AMD) and macular degeneration, cerebral palsy,trigeminal neuralgia, migraine, Alzheimer's disease, Huntington'schorea, Parkinson's disease, Creutzfeldt-Jakob's disease, paraneoplasticpolyneuritis, Friedreich disease, delirium, dementia and amnestic andother cognitive disorders (delirium; dementia, such as dementia ofAlzheimer's type, vascular dementia, dementia due to HIV disease,dementia due to head trauma, dementia due to Parkinson's disease,dementia due to Huntington's disease, dementia due to Pick's disease,dementia due to Creutzfeldt-Jakob disease, dementia due to generalmedical condition, substance-induced dementia, dementia due to multipleetiologies, dementia NOS (hereinafter “not otherwise specified” isabbreviated NOS); amnestic disorders, (such as amnestic disorder due togeneral medical condition, substance-induced amnestic disorder, amnesticdisorder NOS; cognitive disorder NOS); ischemic or hemorrhagic cerebralvascular incidents including stroke and traumatic brain injury (TBI),phakomatoses (particularly neurofibromatoses), amyotrophic lateralsclerosis, spinal muscular atrophy, schizophrenia, mood disorders (suchas depressive disorder, including major depressive disorder—singleepisode or recurrent, dysthymic disorder, depressive disorder NOS;bipolar disorder, including. bipolar I disorder, bipolar II disorder,cyclothymic disorder, bipolar disorder NOS, mood disorder due to generalmedical condition, substance-induced mood disorder, mood disorder NOS),drug withdrawal symptoms, stuttering, autism, autism spectrum disorders,convulsive disorders such as epilepsy; anxiety disorders (panic disorderwithout agoraphobia, panic disorder with agoraphobia, agoraphobiawithout history of panic disorder, specific phobia, social phobia,obsessive compulsive disorder, posttraumatic stress disorder, acutestress disorder, generalized anxiety disorder, anxiety disorder due to amedical condition, substance induced anxiety disorder, anxiety disordernot otherwise specified (NOS)), mood disorders, sleep disorders (primarysleep disorder, including. primary insomnia, primary hypersomnia,narcolepsy, breathing-related sleep disorder, circadian rhythm sleepdisorder, dyssomnia NOS; parasomnia, including. nightmare disorder,sleep terror disorder, sleepwalking disorder, parasomnia NOS; sleepdisorder secondary to another mental disorder, including sleep disordersecondary to anxiety, mood disorder and/or other mental disorder; sleepdisorder due to general medical condition and substance-induced sleepdisorder), attention deficit, attention deficit hyperactivity, anddisruptive behavior disorders (attention deficit/hyperactivitydisorder—combined type, predominantly inattentive type and predominantlyhyperactive—impulsive type; attention deficit/hyperactivity disorderNOS; conduct disorder, oppositional defiant disorder and disruptivebehavior disorder NOS), substance related disorders, eating disorderssuch as anorexia and bulimia.

In certain embodiments, compounds of Formulae I-II and pharmaceuticallyacceptable salts thereof are useful in treatment, prevention,amelioration or management of diseases or disorders, including, but notlimited to disorders of central nervous system, such as epilepsy,ischaemic or hemorrhagic cerebral vascular accidents, neurodegenerativediseases, such as Charcot-Marie-Tooth disease or Friedreich disease,phakomatoses, in particular neurofibromatoses, neuropathic diseases,such as deficiency neuropathy, in particular of the alcoholic kind,toxic or drug-induced neuropathy, particularly by vincristine,neuropathy associated with a metabolic disturbance such as diabetes,neuropathy associated with an inflammatory process, in particularGuillain-Barre syndrome, infectious neuropathic diseases, in particularHerpes zoster, and radiculoneuropathic diseases, paraneoplasticpolyneuritis, multiple sclerosis, amyotrophic lateral sclerosis, spinalmuscular atrophy, schizophrenia, depression, brain tumours, Parkinson'sdisease, and dementias, such as Alzheimer's disease, Pick's disease orvascular dementia, multiple sclerosis, nerve regeneration,neurodegenerative diseases, muscle relaxation in spinal spasticity,cerebral palsy, trigeminal neuralgia, migraine, Alzheimer's disease,pain, drug withdrawal symptoms and convulsive disorders such asepilepsy.

In certain embodiments, compounds or compositions of this invention areuseful in treatment of mental disorders, such as anxiety, depression,epilepsy, obsessive compulsive disorders, attention deficit disorder(ADD), attention deficit disorder with hyperactivity (ADHD), sleepdisorders, eating disorders such as anorexia and bulimia, panic attacks,and other mental disorders.

In some embodiments, the central system disorder is selected frommultiple sclerosis, muscle relaxation in spinal spasticity, cerebralpalsy, trigeminal neuralgia, migraine, Alzheimer's disease, Huntington'schorea, Parkinson's disease, Creutzfeldt-Jakob's disease,neurodegenerative diseases, delirium, dementia, amnestic disorders,cognitive disorders; ischemic or hemorrhagic cerebral vascular incidentsincluding stroke and traumatic brain injury (TBI), phacomatoses,amyotrophic lateral sclerosis, spinal muscular atrophy, schizophrenia,mood disorders, depression, drug withdrawal, symptoms, stuttering,autism, autism spectrum disorders, convulsive disorders, epilepsy,anxiety disorders, sleep disorders, attention deficit disorder,attention deficit hyperactivity disorder, disruptive behavior disorders,and substance related disorders.

In some embodiments the compounds of Formulae I-II are used to treatneuropathic disorders is selected from diabetic neuropathy, drug-inducedneuropathy, inflammatory neuropathy, peripheral neuropathy, HIV-inducedneuralgia and post-herpetic neuralgia, neuropathies associated withenzyme deficiency as in Fabry's disease and Krabbe's disease, hereditarymotor and sensory neuropathies such as Charcot-Marie-Tooth disease.

In some embodiments the compounds of Formulae I-II are used to treatcentral nervous system disorders selected from cognitive disorders,delirium; dementia, dementia of Alzheimer's type, vascular dementia,dementia due to HIV disease, dementia due to head trauma, dementia dueto Parkinson's disease, dementia due to Huntington's disease, dementiadue to Pick's disease, dementia due to Creutzfeldt-Jakob disease, andamnestic disorders.

In some embodiments the compounds of Formulae I-II are used to treatmultiple sclerosis.

In some embodiments the compounds of Formulae I-II are used to treatepilepsy.

In some embodiments the compounds of Formulae I-II are used to treatcentral nervous system disorders is selected from anxiety disorders,panic disorder without agoraphobia, panic disorder with agoraphobia,agoraphobia without history of panic disorder, specific phobia, socialphobia, obsessive compulsive disorder, post-traumatic stress disorder,acute stress disorder, generalized anxiety disorder, anxiety disorderdue to a medical condition, substance induced anxiety disorder, andanxiety disorder not otherwise specified (NOS).

In some embodiments the compounds of Formulae I-II are used to treatamyotrophic lateral sclerosis.

In some embodiments the compounds of Formulae I-II are used to treatspinal muscular atrophy.

In some embodiments the compounds of Formulae I-II are used to treatcentral nervous system disorders selected from mood disorders,depressive disorder, including major depressive disorder—single episodeor recurrent, dysthymic disorder, depressive disorder NOS; bipolardisorder, including. bipolar I disorder, bipolar II disorder,cyclothymic disorder, bipolar disorder NOS, mood disorder due to generalmedical condition, substance-induced mood disorder, and mood disorderNOS.

In some embodiments the compounds of Formulae I-II are used to treatinflammatory disorders. In one aspect, the inflammatory disorder isrheumatoid arthritis.

In some embodiments the compounds of Formulae I-II are used to treat gutmotility disorders. In one aspect, the gut motility disorder isirritable bowel syndrome.

In certain embodiments, compounds of Formulae I-II are useful intreatment of diseases or disorders, including, but not limited tocardiovascular disorders such as hypertension.

In certain embodiments, compounds of Formulae I-II are useful as ananalgesic or antidepressant.

In certain embodiments, compounds of Formulae I-II are useful in thetreatment or prevention retinal degenerations and photo-induced damageto the retina including photoretinitis, retinitis pigmentosa,age-related macular degeneration (AMD) and macular degeneration.

Combination Therapy

In certain embodiments, compounds of Formulae I-II provided herein areadministered in combination with one or more other active ingredients,such as other agents effective for CNS disorders or mental disorders.Such agents include, but are not limited to the following: serotoninreceptor (including., 5-HT1A) agonists and antagonists; neurokininreceptor antagonists or corticotropin releasing factor receptor (CRF1)antagonists; melatonin receptor agonists; and nicotinic agonists,muscarinic agents, acetylcholinesterase inhibitors and dopamine receptoragonists.

In certain embodiments, the other active agents are arylpiperazines, forexample buspirone, gepirone, ipsapirone and tondospirone; benzodiazepinederivatives such as alprazolam, bromazepam, camazepam, chlordiazepoxide,clobazam, clorazepate, chotiazepam, cloxazolam, diazepam, ethylloflazepate, etizolam, fluidazepam, flutazolam, flutoprazepam,halazepam, ketazolam, lorazepam, loxapine, medazepam, metaclazepam,mexazolam, nordazepam, oxazepam, oxazolam, pinazepam, prazepam andtofisopam; carbamates such as cyclarbamate, emylcamate,hydroxyphenamate, meprobamate, phenprobamate and tybamate; and otherssuch as alpidem, benzoctamine, captodiamine, chlormezanone, flesinoxan,fluoresone, glutamic acid, hydroxyzine, lesopitron, mecloralurea,mephenoxalone, mirtazepine, oxanamide, phenaglycodol, suriclone andzatosetron.

In certain embodiments, the other active agent is fluoxetine,paroxetine, sertraline, citalopram, orfluvoxamine, venlafaxine,mirtazapine, nefazodone, trazodone, bupropion, lithium, valproic acidcarbamazepine, neurontin, lamictal, ziprasidone, risperidone,quetiapine, phenelzine, tranylcypromine, amitriptyline, protriptyline,desipramine, nortriptyline, trimipramine, perphenazine, maprotiline,mirtazapine, methylphenidate or dextroamphetamine.

In certain embodiments, the other active agent is an antidepressant,such as a tricyclic antidepressant (“TCA”), a selective serotoninreuptake inhibitor (“S SRI”), a serotonin and noradrenaline reuptakeinhibitor (“SNRI”), a dopamine reuptake inhibitor (“DRI”), anoradrenaline reuptake inhibitor (“NRI”), a dopamine and noradrenalinereuptake inhibitor (“DNRI”), a monoamine oxidase inhibitor (“MAOI”), analpha-2-receptor blocker or another antidepressant.

Exemplary TCAs include, but are not limited to, amitriptyline,amoxapine, clomipramine, desipramine, doxepin, imipramine, maprotiline,nortriptyline, protriptyline, and trimipramine.

Exemplary SSRIs include, but are not limited to, sertraline, sertralinemetabolite demethylsertraline, fluoxetine, norfluoxetine (fluoxetinedesmethyl metabolite), fluvoxamine, paroxetine, citalopram, citaloprammetabolite desmethylcitalopram, escitalopram, d,l-fenfluramine,femoxetine, ifoxetine, cyanodothiepin, litoxetine, cericlamine anddapoxetine.

Exemplary NRIs include, but are not limited to, reboxetine and allisomers of reboxetine, i.e., (R/R,S/S,R/S,S/R), desipramine,maprotiline, lofepramine, oxaprotiline, fezolamine, atomoxetine,nomifensine, viloxazine, or mianserin.

Exemplary SNRIs include, but are not limited to, venlafaxine,venlafaxine metabolite 0-desmethylvenlafaxine, clomipramine,clomipramine metabolite desmethylclomipramine, duloxetine, milnacipran,imipramine, and nefazaodone.

Exemplary MAOIs include, but are not limited to, phenelzine,tranylcypromine, isocarboxazid, and selegiline.

Exemplary alpha-2-receptor blockers include, but are not limited to,mirtazapine.

Other useful antidepressants include buproprion, buproprion metabolitehydroxybuproprion and trazodone.

In one embodiment, in the methods provided herein, “compounds orcompositions of this invention are used as an unsolvated or a freecompound.

In another embodiment, in the methods provided herein, compounds orcompositions of this invention are used as a salt, such as ahydrochloride salt.

In another embodiment, in the methods provided herein, compounds orcompositions of this invention are used as a solvate.

Formulations

Compounds of the invention are administered orally in a total daily doseof about 0.01 mg/kg/dose to about 100 mg/kg/dose, alternately from about0.1 mg/kg/dose to about 10 mg/kg/dose. The use of time-releasepreparations to control the rate of release of the active ingredient maybe employed. The dose may be administered in as many divided doses as isconvenient. When other methods are used (including. intravenousadministration), compounds are administered to the affected tissue at arate from 0.05 to 10 mg/kg/hour, alternately from 0.1 to 1 mg/kg/hour.Such rates are easily maintained when these compounds are intravenouslyadministered as discussed below.

For the purposes of this invention, the compounds may be administered bya variety of means including orally, parenterally, by inhalation spray,topically, or rectally in formulations containing pharmaceuticallyacceptable carriers, adjuvants and vehicles. The term parenteral as usedhere includes subcutaneous, intravenous, intramuscular, andintraarterial injections with a variety of infusion techniques.Intraarterial and intravenous injection as used herein includesadministration through catheters. Oral administration is generallyemployed.

Pharmaceutical compositions containing the active ingredient may be inany form suitable for the intended method of administration. When usedfor oral use for example, tablets, troches, lozenges, aqueous or oilsuspensions, dispersible powders or granules, emulsions, hard or softcapsules, syrups or elixirs may be prepared. Compositions intended fororal use may be prepared according to any method known to the art forthe manufacture of pharmaceutical compositions and such compositions maycontain one or more agents including sweetening agents, flavoringagents, coloring agents and preserving agents, in order to provide apalatable preparation. Tablets containing the active ingredient inadmixture with non-toxic pharmaceutically acceptable excipient which aresuitable for manufacture of tablets are acceptable. These excipients maybe, for example, inert diluents, such as calcium or sodium carbonate,lactose, calcium or sodium phosphate; granulating and disintegratingagents, such as maize starch, or alginic acid; binding agents, such asstarch, gelatin or acacia; and lubricating agents, such as magnesiumstearate, stearic acid or talc. Tablets may be uncoated or may be coatedby known techniques including microencapsulation to delay disintegrationand adsorption in the gastrointestinal tract and thereby provide asustained action over a longer period. For example, a time delaymaterial such as glyceryl monostearate or glyceryl distearate alone orwith a wax maybe employed.

Formulations for oral use may be also presented as hard gelatin capsuleswhere the active ingredient is mixed with an inert solid diluent, forexample calcium phosphate or kaolin, or as soft gelatin capsules whereinthe active ingredient is mixed with water or an oil medium, such aspeanut oil, liquid paraffin or olive oil.

Aqueous suspensions of the invention contain the active materials inadmixture with excipients suitable for the manufacture of aqueoussuspensions. Such excipients include a suspending agent, such as sodiumcarboxymethylcellulose, methylcellulose, hydroxypropyl methylcellulose,sodium alginate, polyvinylpyrrolidone, gum tragacanth and gum acacia,and dispersing or wetting agents such as a naturally occurringphosphatide (including., lecithin), a condensation product of analkylene oxide with a fatty acid (including., polyoxyethylene stearate),a condensation product of ethylene oxide with a long chain aliphaticalcohol (including., heptadecaethyleneoxycetanol), a condensationproduct of ethylene oxide with a partial ester derived from a fatty acidand a hexitol anhydride (including., polyoxyethylene sorbitanmonooleate). The aqueous suspension may also contain one or morepreservatives such as ethyl or n-propyl p-hydroxy-benzoate, one or morecoloring agents, one or more flavoring agents and one or more sweeteningagents, such as sucrose or saccharin.

Oil suspensions may be formulated by suspending the active ingredient ina vegetable oil, such as arachis oil, olive oil, sesame oil or coconutoil, or in a mineral oil such as liquid paraffin. The oral suspensionsmay contain a thickening agent, such as beeswax, hard paraffin or cetylalcohol. Sweetening agents, such as those set forth above, and flavoringagents may be added to provide a palatable oral preparation. Thesecompositions may be preserved by the addition of an antioxidant such asascorbic acid.

Dispersible powders and granules of the invention suitable forpreparation of an aqueous suspension by the addition of water providethe active ingredient in admixture with a dispersing or wetting agent, asuspending agent, and one or more preservatives. Suitable dispersing orwetting agents and suspending agents are exemplified by those disclosedabove. Additional excipients, for example sweetening, flavoring andcoloring agents, may also be present.

The pharmaceutical compositions of the invention may also be in the formof oil-in-water emulsions. The oily phase may be a vegetable oil, suchas olive oil or arachis oil, a mineral oil, such as liquid paraffin, ora mixture of these. Suitable emulsifying agents includenaturally-occurring gums, such as gum acacia and gum tragacanth,naturally occurring phosphatides, such as soybean lecithin, esters orpartial esters derived from fatty acids and hexitol anhydrides, such assorbitan monooleate, and condensation products of these partial esterswith ethylene oxide, such as polyoxyethylene sorbitan monooleate. Theemulsion may also contain sweetening and flavoring agents.

Syrups and elixirs may be formulated with sweetening agents, such asglycerol, sorbitol or sucrose. Such formulations may also contain ademulcent, a preservative, a flavoring or a coloring agent.

The pharmaceutical compositions of the invention may be in the form of asterile injectable preparation, such as a sterile injectable aqueous oroleaginous suspension. This suspension may be formulated according tothe known art using those suitable dispersing or wetting agents andsuspending agents which have been mentioned above. The sterileinjectable preparation may also be a sterile injectable solution orsuspension in a non-toxic parenterally acceptable diluent or solvent,such as a solution in 1,3-butanediol or prepared as a lyophilizedpowder. Among the acceptable vehicles and solvents that may be employedare water, Ringer's solution and isotonic sodium chloride solution. Inaddition, sterile fixed oils may conventionally be employed as a solventor suspending medium. For this purpose any bland fixed oil may beemployed including synthetic mono- or diglycerides. In addition, fattyacids such as oleic acid may likewise be used in the preparation ofinjectables.

The amount of active ingredient that may be combined with the carriermaterial to produce a single dosage form will vary depending upon thehost treated and the particular mode of administration. For example, atime-release formulation intended for oral administration to humans maycontain approximately 1 to 1000 mg of active material compounded with anappropriate and convenient amount of carrier material which may varyfrom about 5 to about 95% of the total compositions. The pharmaceuticalcomposition can be prepared to provide easily measurable amounts foradministration. For example, an aqueous solution intended forintravenous infusion should contain from about 3 to 330 .mu.g of theactive ingredient per milliliter of solution in order that infusion of asuitable volume at a rate of about 30 mL/hr can occur.

As noted above, formulations of the present invention suitable for oraladministration may be presented as discrete units such as capsules,cachets or tablets each containing a predetermined amount of the activeingredient; as a powder or granules; as a solution or a suspension in anaqueous or non-aqueous liquid; or as an oil-in-water liquid emulsion ora water-in-oil liquid emulsion. The active ingredient may also beadministered as a bolus, electuary or paste.

A tablet may be made by compression or molding, optionally with one ormore accessory ingredients. Compressed tablets may be prepared bycompressing in a suitable machine the active ingredient in a freeflowing form such as a powder or granules, optionally mixed with abinder (including., povidone, gelatin, hydroxypropylmethyl cellulose),lubricant, inert diluent, preservative, disintegrant (including., sodiumstarch glycolate, cross-linked povidone, cross-linked sodiumcarboxymethyl cellulose) surface active or dispersing agent. Moldedtablets may be made by molding in a suitable machine a mixture of thepowdered compound moistened with an inert liquid diluent. The tabletsmay optionally be coated or scored and may be formulated so as toprovide slow or controlled release of the active ingredient thereinusing, for example, hydroxypropyl methylcellulose in varying proportionsto provide the desired release profile. Tablets may optionally beprovided with an enteric coating, to provide release in parts of the gutother than the stomach. This is particularly advantageous with thecompounds of Formula I when such compounds are susceptible to acidhydrolysis.

Formulations suitable for topical administration in the mouth includelozenges comprising the active ingredient in a flavored base, usuallysucrose and acacia or tragacanth; pastilles comprising the activeingredient in an inert base such as gelatin and glycerin, or sucrose andacacia; and mouthwashes comprising the active ingredient in a suitableliquid carrier.

Formulations for rectal administration may be presented as a suppositorywith a suitable base comprising for example cocoa butter or asalicylate.

Formulations suitable for vaginal administration may be presented aspessaries, tampons, creams, gels, pastes, foams or spray formulationscontaining in addition to the active ingredient such carriers as areknown in the art to be appropriate.

Formulations suitable for parenteral administration include aqueous andnon-aqueous isotonic sterile injection solutions which may containantioxidants, buffers, bacteriostats and solutes which render theformulation isotonic with the blood of the intended recipient; andaqueous and non-aqueous sterile suspensions which may include suspendingagents and thickening agents. The formulations may be presented inunit-dose or multi-dose sealed containers, for example, ampoules andvials, and may be stored in a freeze-dried (lyophilized) conditionrequiring only the addition of the sterile liquid carrier, for examplewater for injections, immediately prior to use. Injection solutions andsuspensions may be prepared from sterile powders, granules and tabletsof the kind previously described.

Suitable unit dosage formulations are those containing a daily dose orunit, daily sub-dose, or an appropriate fraction thereof, of a compoundof Formula I.

The formulations of the present invention may include any of thecompounds of Formula I or pharmaceutically acceptable salts, solvates orprodrugs thereof as the only pharmaceutically active agent.Alternatively, the formulations may include one or more further activeagents including those described under the section Combination Therapy.

It will be understood, however, that the specific dose level for anyparticular patient will depend on a variety of factors including theactivity of the specific compound employed; the age, body weight,general health, sex and diet of the individual being treated; the timeand route of administration; the rate of excretion; other drugs whichhave previously been administered; and the severity of the particulardisease undergoing therapy, as is well understood by those skilled inthe art.

The invention also provides a kit comprising a therapeutically effectiveamount of a compound of Formula I, or a pharmaceutically acceptablesalt, solvate, or prodrug thereof, and instructions for treating a humanpatient suffering from conditions amenable to modulation of the GABA_(A)receptor complex; or increasing endogenous neurosteroid and neuroactivesteroid levels; CNS disorders; PNS disorders; or inflammatory conditionsas described above. The kit may also include one or more further activeagents including those described under the section Combination Therapy.

Synthetic Chemistry Examples

Standard procedures and chemical transformation and related methods arewell known to one skilled in the art, and such methods and procedureshave been described, for example, in standard references such asFiesers' Reagents for Organic Synthesis, John Wiley and Sons, New York,N.Y., 2002; Organic Reactions, vols. 1-83, John Wiley and Sons, NewYork, N.Y., 2006; March J. and Smith M.: Advanced Organic Chemistry, 6thed., John Wiley and Sons, New York, N.Y.; and Larock R. C.:Comprehensive Organic Transformations, Wiley-VCH Publishers, New York,1999.

Reactions using compounds having functional groups may be performed oncompounds with functional groups that may be protected. A “protected”compound or derivatives means derivatives of a compound where one ormore reactive site or sites or functional groups are blocked withprotecting groups. Protected derivatives are useful in the preparationof the compounds of the present invention or in themselves; theprotected derivatives may be the biologically active agent. An exampleof a comprehensive text listing suitable protecting groups may be foundin T. W. Greene, Protecting Groups in Organic Synthesis, 3rd edition,John Wiley & Sons, Inc. 1999.

A compound of Formulae I-II can be synthesized as depicted in scheme 1:

Protection of the amino group of p-Chloro aniline 1 by means known inthe art is achieved by treating the amine 1 with Di-t-Butyl dicarbonate.As described by E. Azim et al. in J. Label. Compds. Radiopharm.XXXIX:907, 1997, ortho lithiation of 2 followed by addition ofbenzaldehyde yields the tertiary alcohol 3. Further benzylic oxidationof 3 followed by hydrolytic cleavage of the amino protective groupprovides compound 4. Addition of methyl Grignard in diethyl ether yieldsthe tertiary alcohol 5. As described by Garratt, P. J et al. inTetrahedron, 45 (3), 829, 1989, Alcohol 5 is reacted with diphenylcyanocarbonimidate to give compound 6. Further reaction with deuteratedethylamine in refluxing isopropyl alcohol yields compounds of Formula I.

A compound of Formulae I-II can also be synthesized from intermediate 5as depicted in scheme 2:

As described by E. Azim et al. in J. Label. Compds. Radiopharm.XXXIX:907, 1997, treating intermediate 5 with deuterated ethylisothiocyanate at 60.degree. C. in toluene yields the thiourea 7. Asdescribed by S-W You et al. in Bull. Korean Chem. Soc. 2001, (22), 11,1270, thiourea 7 is reacted with dicyclohexylcarbodiimide in refluxingacetonitrile to yield compounds of Formula I.

The Compound numbers correspond to the Example numbers provided in Table1 below.

TABLE 1 Example number Example name Example Structure 16-chloro-N-(ethyl-d₅)-4-methyl-4-phenyl- 4H-3,1-benzoxazin-2-amine

2 6-chloro-N-(ethyl-d₅)-4-methyl-4-(phenyl-d₅)-4H-3,1-benzoxazin-2-amine

3 6-chloro-N-(ethyl-d₅)-4-(methyl-d₃)-4-(phenyl-d₅)-4H-3,1-benzoxazin-2-amine

4 6-chloro-N-(ethyl-1,1-d2)-4-methyl-4- phenyl-4H-3,1-benzoxazin-2-amine

5 6-chloro-N-ethyl-4-(methyl-d3)-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amine

6 6-chloro-N-ethyl-4-methyl-4-(phenyl-d5)- 4H-3,1-benzoxazin-2-amine

7 6-chloro-N-ethyl-4-(methyl-d3)-4-phenyl- 4H-3,1-benzoxazin-2-amine

Example 1 Synthesis of6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amineSynthesis of 1-(2-amino-5-chlorophenyl)-1-phenyethan-1-ol

To 2-amino-5-chlorobenzophenone (2.34 mmols, 541 mgs) in diethyl ether(10 mL) under nitrogen atmosphere at 0.degree. C. was added dropwisemethylmagnesium iodide (3.12 mL, 3.0M in diethyl ether). The reactionmixture was stirred and left to warm to room temperature. After 5 hours,the mixture was cooled to 0.degree. C. and ice chips were carefullyadded followed by cold water. Brine was added to separate the phases.The ether layer was separated. The aqueous layer was extracted with anequal amount of ether. The combined ether layers were dried overmagnesium sulfate, filtered and concentrated under vacuum to yield thetertiary alcohol (2.14 mmols, 530 mgs). MS: (M+H) 248.

Synthesis ofN-(6-chloro-4-methyl-4-phenyl-1,4-dihydro-2H-benzo[d][1,3]oxazin-2-yliden-e)cyanamide

Diphenyl cyanocarbonimidate (10.3 mmols, 2.53 g) and1-(2-amino-5-chlorophenyl)-1-phenyethan-1-ol (9.36 mmols, 2.32 g) wereadded to isopropanol (40 mL) and the reaction mixture was refluxed for24 hours under nitrogen atmosphere. The solvent was removed under vacuumand the residue was purified by flash chromatography (silica gel)(Eluent 2% MeOH/CH.sub.2CL.sub.2) to yieldN-(6-chloro-4-methyl-4-phenyl-1,4-dihydro-2H-benzo[d][1,3]oxazin-2-yliden-e)cyanamideas a white solid (2.7 mmols, 800 mgs). MS: (M−) 296.

Synthesis of6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amine

d.sub.5-ethylamine hydrochloride (0.69 mmols, 59 mgs) (99% deuteriumincorporation) was added to a flask containingN-(6-chloro-4-methyl-4-phenyl-1,4-dihydro-2H-benzo[d][1,3]oxazin-2-yliden-e)cyanamide(100 mgs, 0.35 mmol) and Hunig's base (0.7 mmol, 0.12 mL) in isopropanol(1 mL). The mixture was stirred at reflux for 12 hours. Additionald.sub.5-ethylamine hydrochloride (0.69 mmol, 59 mgs) and Hunig's base(0.7 mmol, 0.12 mL) were added and the reaction mixture was stirred atreflux for another 12 hours. The solvent was then removed under vacuumand the residue purified by reverse phase (Agilent C18 eclipse pluscolumn) HPLC to yield6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amine(0.11 mmols, 33 mgs) as a waxy solid. MS: (M+H) 306.

Example 2 Synthesis of6-chloro-N-(ethyl-d.sub.5)-4-methyl-4-(phenyl-d.sub.5)-4H-3,1-benzoxazin-2-amineSynthesis of tert-butyl(4-chloro-2-(hydroxy(phenyl-d5)methyl)phenyl)carbamate

A solution of tert-butyl (4-chlorophenyl)carbamate (2.03 g, 8.92 mmols)dissolved in 52 mL of dry THF at −78.degree. C. was treated with 16 mL(22.4 mmol, 2.5 eq.) of a 1.4M solution of sec-butyllithium incyclohexane added via syringe over 25 min. The reaction mixture wasallowed to warm to −25.degree. C. and was treated withd.sub.6-benzaldehyde (900 .mu.L) (98% deuterium incorporation). Uponaddition, the reaction mixture was allowed to warm to room temperature.The reaction mixture was then cooled to 0.degree. C., quenched with 26mL of a saturated aqueous NH.sub.4C1 solution and 50 mL of water. Theaqueous layer was washed with EtOAc (50 mL). Pooled organic layers werewashed with brine, dried over MgSO.sub.4, filtered and concentrated togive 3.4 g of a yellow oil. The residual oil was purified by flashsilica gel chromatography (4:1 hexanes/EtOAc) to yield tert-butyl(4-chloro-2-(hydroxy(phenyl-d. sub. 5)methyl)phenyl)carbamate as ayellow oil (2.45 g, 7.24 mmols). MS: (M+H) 339.

Synthesis of tert-butyl(2-(benzoyl-2,3,4,5,6-d5)-4-chlorophenyl)carbamate

A solution of tert-butyl(4-chloro-2-(hydroxy(phenyl-d5)methyl)phenyl)carbamate (1.5 g, 4.41mmol) was dissolved in 40 mL of CH.sub.2C1.sub.2 and treated with NaOAc(1.14 g), Celite (1.82 g) and PCC (1.48 g) added in portions. Theresulting mixture was stirred at room temperature for 90 minutes. Anadditional 500 mg of PCC was added and stirred for an additional hour.The reaction mixture was loaded on a silica gel column and eluted withCH.sub.2C1.sub.2. The collected fractions were evaporated to givetert-butyl (2-(benzoyl-2,3,4,5,6-d5)-4-chlorophenyl)carbamate (1.12 g,3.33 mmols). MS: (M+H) 337.

Synthesis of (2-amino-5-chlorophenyl)(phenyl-d5)methanone

A solution of tert-butyl(2-(benzoyl-2,3,4,5,6-d5)-4-chlorophenyl)carbamate (1.05 g, 3.12 mmol)in EtOH (17 mL) was treated with a 10% NaOH (2.5 M; 3.4 mL) aqueoussolution added dropwise. The mixture was then refluxed for 24 hours. Anadditional 3 mL of 2.5 N NaOH was added and the reaction mixture wasrefluxed for an additional 7 hours. After cooling to room temperature,the organic solvent removed in vacuo. The residue was diluted withice-water. It was extracted with 75 mL of EtOAc. The phases wereseparated. The aqueous layer was extracted with EtOAc (2.times.40 mL).The combined organic layers were washed with water (50 mL, brine addedto separate phases) and brine. After drying (MgSO.sub.4), the mixturewas filtered and concentrated in vacuo. To yield a red-orange oil thatsolidified on standing (730 mg). The crude reaction mixture was purifiedby flash silica gel chromatography eluting with 100% CH.sub.2C1.sub.2.The product was obtained as a yellow-orange solid (610 mgs, 2.58 mmols).MS: (M+H) 237

Synthesis of 1-(2-amino-5-chlorophenyl)-1-(phenyl-d5)ethan-1-ol

To 2-amino-5-chlorobenzophenone (1.7 mmols, 402 mgs) in diethyl ether(10 mL) under nitrogen atmosphere at 0.degree. C. was added dropwisemethylmagnesium iodide (6.8 mL, 3.0M in diethyl ether). The reactionmixture was stirred and left to warm to room temperature. After 1.5hour, the mixture was cooled to 0.degree. C. and ice chips werecarefully added followed by cold water. Brine was added to separate thephases. The ether layer was separated. The aqueous layer was extractedwith an equal amount of ether. The combined ether layers were dried overmagnesium sulfate, filtered and concentrated under vacuum to yield thetertiary alcohol (1.33 mmols, 335 mgs). MS: (M+H) 253.

Synthesis of1-(4-chloro-2-(1-hydroxy-1-(phenyl-d5)ethyl)phenyl)-3-(ethyl-d5)thiourea

To 1-(2-amino-5-chlorophenyl)-1-(phenyl-d5)ethan-1-ol (167 mgs, 0.67mmols) in toluene (3 mL) was added with d5-ethyl isothiocyanate (0.99mmol, 88 .mu.L). The mixture was stirred at 60.degree. C. for 24 hours.The solvent was removed in vacuo and the residue was purified by flashsilica gel chromatography eluting with 3/1 hexanes/EtOAc to yield theproduct (0.6 mmol, 204 mgs) MS: (M+H) 340.

Synthesis of d.sub.5-ethyl Isothiocyanate Ethyld.sub.5-ethyldithiocarbamate

d.sub.5-ethylamine hydrochloride salt (1.27 g, 14.7 mmols) (99%deuterium incorporation) was suspended in EtOH-free CHCl.sub.3 (8 mL)and cooled in an ice water bath and treated with neat Et.sub.3N (4.1 mL,29.4 mmols) added dropwise via syringe. Neat CS.sub.2 (969 .mu.L, 16.2mmols) was added dropwise via syringe and the cold bath was removed. Thethick mixture stirred at room temperature for 3 h and cooled in anice-salt bath to −10.degree. C. Neat iodoethane (1.2 mL, 15.0 mmols) wasadded to the cold reaction mixture dropwise via syringe. The reactionmixture was allowed to warm to room temperature and stirred overnight.The resulting solution was concentrated in vacuo and the residue wastreated with 60 mL each of EtOAc and a 1M HCl solution. The organiclayer was washed with water (40 mL), dried (MgSO.sub.4), filtered andconcentrated in vacuo, affording 2.07 g of a brown oil.

d.sub.5-Ethyl Isothiocyanate

A flask equipped with a distillation head containing ethyld.sub.5-ethyldithiocarbamate was placed in a sand bath at 150.degree. C.and heated to 230.degree. C. A light yellow liquid was collected as itdistilled off. This liquid was heated at 80.degree. C. to removeethanethiol leaving d.sub.5-ethyl isothiocyanate as a light yellowliquid.

Synthesis of(6-chloro-N-(ethyl-d5)-4-methyl-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amine

To a stirred solution of1-(4-chloro-2-(1-hydroxy-1-(phenyl-d5)ethyl)phenyl)-3-(ethyl-d5)thiourea(100 mgs, 0.29 mmol) in acetonitrile (2 mL) was addeddicyclohexylcarbodiimide (0.45 mmol, 91 mgs). The reaction mixture washeated to reflux for 3 hours. The solvent was evaporated and the residuewas purified by flash silica gel chromatography eluting with 85/15hexanes/EtOAc to yield(6-chloro-N-(ethyl-d5)-4-methyl-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amine.MS: (M+H) 311.

Example 3 Synthesis of6-chloro-N-(ethyl-d.sub.5)-4-(methyl-d.sub.3)-4-(phenyl-d.sub.5)-4H-3,1-b-enzoxazin-2-amine

Following the same steps described in example 2 and substitutingmethylmagnesium iodide with d.sub.3-methylmagnesium iodide (preparedfrom d.sub.3-iodomethane 99.5% deuterium incorporation) provides6-chloro-N-(ethyl-d.sub.5)-4-(methyl-d.sub.3)-4-(phenyl-d.sub.5)--4H-3,1-benzoxazin-2-amine. MS: (M+H) 314.

Example 4 Synthesis of6-chloro-N-(ethyl-1,1-d2)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amine

Following the same steps described in example 1 and substitutingd.sub.5-ethylamine hydrochloride with 1,1-d.sub.2-ethylaminehydrochloride (98% deuterium incorporation) provides6-chloro-N-(ethyl-1,1-d2)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amine.MS: (M+H) 303.

Example 5 Synthesis of6-chloro-N-ethyl-4-(methyl-d3)-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amine

Following the same steps described in example 2 and substitutingd.sub.5-ethylisothiocyanate with ethylisothiocyanate and substitutingmethylmagnesium iodide with d.sub.3-methylmagnesium iodide provides6-chloro-N-ethyl-4-(methyl-d3)-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amine.MS: (M+H) 309.

Example 6 Synthesis of6-chloro-N-ethyl-4-methyl-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amine

Following the same steps described in example 2 and substitutingd.sub.5-ethylisothiocyanate with ethylisothiocyanate provides6-chloro-N-ethyl-4-methyl-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amine. MS:(M+H) 306.

Example 7 Synthesis of6-chloro-N-ethyl-4-(methyl-d3)-4-phenyl-4H-3,1-benzoxazin-2-amine

Following the same steps described in example 2 and substitutingd.sub.5-ethylisothiocyanate with ethylisothiocyanate and substitutingmethylmagnesium iodide with d.sub.3-methylmagnesium iodide andsubstituting d.sub.6-benzaldehyde with benzaldehyde provides6-chloro-N-ethyl-4-(methyl-d3)-4-phenyl-4H-3,1-benzoxazin-2-amine. MS:(M+H) 304.

Example 8 Synthesis of6-chloro-N-(ethyl-d5)-4-(methyl-d3)-4-phenyl-4H-3,1-benzoxazin-2-amine

Following the same steps described in example 1 and substitutingmethylmagnesium iodide with d.sub.3-methylmagnesium iodide provides6-chloro-N-(ethyl-d5)-4-(methyl-d3)-4-phenyl-4H-3,1-benzoxazin-2-amine.

Example 9 Synthesis of6-chloro-N-(ethyl-1,1-d2)-4-methyl-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amin-e

Following the same steps described in example 2 and substitutingd.sub.5-ethylisothiocyanate with 1,1-d.sub.2-ethylisothiocyanate(prepared from 1,1-d.sub.2ethylamine hydrochloride (98% deuteriumincorporation)) provides6-chloro-N-(ethyl-1,1-d2)-4-methyl-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amin-e.

Example 10 Synthesis of6-chloro-N-(ethyl-1,1-d2)-4-(methyl-d3)-4-(phenyl-2-d)-4H-3,1-benzoxazin-2-amine

Following the same steps described in example 1 and substitutingmethylmagnesium iodide with d.sub.3-methylmagnesium iodide andd.sub.5-ethylamine hydrochloride with 1,1-d.sub.2-ethylaminehydrochloride (prepared from 1,1-d.sub.2-iodoethane (98% deuteriumincorporation)) provides6-chloro-N-(ethyl-1,1-d.sub.2)-4-(methyl-d.sub.3)-4-(phenyl-d.sub.2)-4H-3-,1-benzoxazin-2-amine.

Example 11 Synthesis of6-chloro-N-(ethyl-d.sub.2)-4-(methyl-d.sub.3)-4-(phenyl-d.sub.5)-4H-3,1-b-enzoxazin-2-amine

Following the same steps described in example 3 and substitutingd.sub.5-ethyl-isothiocyanate with 1,1-d.sub.2-ethylisothiocyanateprovides6-chloro-N-(ethyl-1,1-d.sub.2)-4-(methyl-d.sub.3)-4-(phenyl-d.sub.5)-4-3,-1-benzoxazin-2-amine.

Biological Examples

A. Evaluation of Metabolic Stability

Compounds were evaluated for liver microsome metabolic stability atEurofins/Cerep (St. Charles, Mo.). Standard conditions for Cerep's livermicrosome stability assay as described by Obach et al in J. Pharmacol.Exp. Ther. 283, 46, 1997, were used. Test compounds at a concentrationof 0.1 .mu.M were incubated for up to 60 minutes in duplicate. Themicrosomal protein concentration was 0.1 mg/mL. The parent compound wasdetected by HPLC-MS/MS analysis. The percent compound remaining wascalculated by comparing the peak area of the parent compound at eachtime point to time zero. Half-life was estimated from the slope of theinitial linear range of the logarithmic curve of parent compoundremaining vs. time, assuming first order kinetics. The apparentintrinsic clearance was further calculated from the half-life value forassays with microsomes.

The results of the liver human microsomes stability study are shown inTable 2 below:

TABLE 2 Half-life (minutes) Compound Experiment 1 Experiment 2 AverageEtifoxine 23 21.9 22 Example 1 39.7 41.8 41

The compounds described as examples 6 and 7 were tested under the sameconditions, but with a different lot of human liver microsomes. Bothdisplayed an average half-life of 18 minutes.

The results of the rat liver microsomes stability study are shown inTable 3 below:

TABLE 3 Half-life (minutes) Compound Experiment 1 Experiment 2 AverageEtifoxine 7.7 7.4 8 Example 1 13.8 13.8 14

The results of the liver human microsome stability study reveal that thehalf-life of Example 1 is about 86% longer than that of etifoxine.

The results of the rat liver microsome stability study reveal that thehalf-life of Example 1 is about 75% longer than that of etifoxine.

B. Evaluation of Pharmacokinetics in Rats for Compound Example 1

Compounds were evaluated for pharmacokinetic profiles in maleSprague-Dawley rats at Shanghai Chempartner, Shanghai, China. Etifoxinehydrochloride and the hydrochloride salt of the compound described inexample 1 were dosed to Sprague-Dawley rats via oral gavage (PO). Eachcompound was administered at a dose of 50 mg/kg to three rats (N=3rats/compound; total 6 rats in the study). Each compound was formulatedin 70/30 Saline/PEG400 at a concentration of 5 mg/mL (10 mL/kg injectionvolume/rat). Blood samples were collected from each rat at 10, 20, 30,45 minutes and 1, 2, 4 and 12 hours post-dose. Blood samples were put onice and centrifugated to obtain plasma. Plasma samples were analyzed forconcentrations of the dosed compound at each time point by LC-MS/MSusing an AB-Sciex API-400 mass spectrometer. The lower limit ofquantitation of each compound was 1 ng/mL. Pharmacokinetic parameterswere determined by non-compartmental analysis using WinNonlin 6.2software.

FIG. 1. Shows averaged data for administered etifoxine hydrochloride andthe hydrochloride salt of the compound described in example 1. Table 4,below, shows the average AUC.sub.0-12 and C.sub.maxobserved foretifoxine hydrochloride and the hydrochloride salt of the compounddescribed in example 1.

TABLE 4 Compound AUC₀₋₁₂ (hr * ng/mL) C_(max) (ng/mL) Etifoxinehydrochloride 3380 1140 Example 1 hydrochloride 8337 1930

As can be seen from Table 4, the AUC.sub.0-12 and C.sub.max of thehydrochloride salt of the compound described in example 1 are 2.5 timesand 1.7 times greater than etifoxine hydrochloride. These resultsindicate decreased pre-systemic metabolism resulting in higherbioavailability of unmetabolized drug. Decreasing pre-systemicmetabolism may result in lesser inter and intra-variability. Increasingdrug exposure may result in reduced dosing frequency as minimal drugtherapeutic level may be achieved for longer period of times. Increasingdrug exposure also allows for dose lowering resulting in less potentialadverse events as similar drug plasma levels can be achieved with alower dose. The data on mean plasma concentration versus time are shownin FIG. 1.

The various features and embodiments of the present invention, referredto in individual sections above apply, as appropriate, to othersections, mutatis mutandis. Consequently features specified in onesection may be combined with features specified in others sections, asappropriate.

The patents and publications listed herein describe the general skill inthe art and are hereby incorporated by reference in their entireties forall purposes and to the same extent as if each was specifically andindividually indicated to be incorporated by reference. In the case ofany conflict between a cited reference and this specification, thespecification shall control. In describing embodiments of the presentapplication, specific terminology is employed for the sake of clarity.However, the invention is not intended to be limited to the specificterminology so selected. Nothing in this specification should beconsidered as limiting the scope of the present invention. All examplespresented are representative and non-limiting. Without furtherdescription, it is believed that one of ordinary skill in the art can,using the preceding description and the illustrative examples, make andutilize the compounds of the present invention and practice the claimedmethods. It is therefore to be understood that, within the scope of theclaims and their equivalents, the invention may be practiced otherwisethan as specifically described.

It would be appreciated by those skilled in the art that various changesand modifications can be made to the illustrated embodiments withoutdeparting from the spirit of the present invention. All suchmodifications and changes are intended to be within the scope of thepresent invention except as limited by the scope of the appended claims.

What is claimed is:
 1. A compound of Formula I:

or a pharmaceutically acceptable salt, solvate or prodrug thereof,wherein: each X¹, X² and X³ is independently hydrogen or deuterium. 2.The compound of claim 1 wherein the compound is:6-chloro-N-(ethyl-d₅)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amine,6-chloro-N-(ethyl-d₅)-4-methyl-4-(phenyl-d_(A))-4H-3,1-benzoxazin-2-amine,6-chloro-N-(ethyl-d5)-4-(methyl-d3)-4-(phenyl-d5)-4H-3,1-benzoxazin-2-amineor 6-chloro-N-(ethyl-1,1-d2)-4-methyl-4-phenyl-4H-3,1-benzoxazin-2-amineor a pharmaceutically acceptable salt, solvate or prodrug thereof. 3.The compound of claim 1, wherein said compound is an enantiomericallypure S-etifoxine analog, or a pharmaceutically acceptable salt, solvateor prodrug thereof.
 4. The compound of claim 1, wherein any atom notdesignated as deuterium is present at its natural isotopic abundance. 5.A pharmaceutical composition comprising the compound of claim 1 and apharmaceutically acceptable excipient.
 6. A method of modulating theGABA_(A) receptor complex in a subject in need thereof comprisingadministering to said subject an effective amount of the compound ofclaim
 1. 7. A method of increasing endogenous neurosteroid and/orneuroactive steroid levels in a subject in need thereof comprisingadministering to said subject an effective amount of the compound ofclaim
 1. 8. The compound of claim 1, wherein a deuterium is present atan abundance that is at least 3340 times greater than the naturalabundance of deuterium.
 9. The compound of claim 1, wherein saidcompound is an enantiomerically pure R-etifoxine analog, or apharmaceutically acceptable salt, solvate or prodrug thereof.